Internal combustion engines such as, but not limited to, diesel and gasoline engines, may include one or more temperature sensors at least partially disposed within the exhaust gas system. These temperature sensors may sense the temperature of the exhaust gas and may be used, at least in part, by an engine control system to adjust one or more properties of the engine such as, but not limited to, air/fuel ratio, boost pressure, timing or the like. Because of the operating environment, the temperature sensors may be exposed to relatively harsh conditions including, but not limited to, vibration, exposure to debris, moisture and corrosive chemicals, large temperature ranges, large temperature gradients, and relatively high continuous use operating temperatures. WO2011094753A2 discloses an exhaust gas temperature sensor comprising a temperature sensor coupled to an end of a mineral insulated cable. The cable is coupled to a stop flange. Furthermore, an anti-vibration sleeve is positioned between the stop flange and the temperature sensor.
Conventional thermocouple devices are difficult to implement in an automotive-style system. These thermocouples are typically unable to operate for the extended life requirement in an automotive setting. This situation is compounded by the increasingly harsh application requirements, which can induce failure of conventional thermocouples. These failures are more likely in sensors with a long probe length or extended high-temperature operation with rapid temperature fluctuation of the fluid in which the probe is positioned.
Upon application of heat to the environment of a conventional sensing device comprising a mineral insulated cable, the outer jacket experiences a rapid temperature increase, while conductors of the mineral insulated cable remain cool. The packed MgO in a mineral insulated cable has namely a very poor thermal conductivity. This leads to tensile stresses on the conductors, which can lead to failure, especially during thermal shock.
These failings of conventional thermocouples create the need for a design solution that enables the use of thermocouples in automotive applications, specifically those requiring long probe length.